JP4183172B2 - Circuit board - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a ceramic circuit board on which electronic components such as semiconductor elements, resistors, and capacitors are placed.
[0002]
[Prior art]
_2. Description of the Related Art Conventionally, circuit boards on which electronic components such as semiconductor elements, resistors, and capacitors are placed are, for example, aluminum oxide (Al ₂ O ₃ ) -based sintered bodies (alumina ceramics) and the like as shown in a plan view in FIG. On a metallized layer made of a refractory metal such as tungsten (W) or molybdenum (Mo) as a mounting portion 22b or wiring conductor 22a for mounting electronic components on the upper main surface of the ceramic insulating substrate 22 For example, iron (Fe) having a metal plating layer made of nickel (Ni), gold (Au) or the like and having an overhanging portion 21a for attachment to an external electric circuit board or the like on the lower main surface A base 21 made of metal such as a Ni-cobalt (Co) alloy is brazed.
[0003]
The base body 21 is made of a metal such as Fe—Ni—Co alloy or copper (Cu) —W, and has a protruding portion 21 a for external mounting provided on the side surface so as to extend outward. For example, the base 21 is provided with a through-hole for inserting a screw into the overhanging portion 21a, and is fixed to the external electric circuit board with a screw.
[0004]
The insulating substrate 22 is bonded to almost the entire surface excluding the protruding portion of the upper main surface of the base 21. The insulating substrate 22 is made of ceramics such as an Al ₂ O ₃ sintered body and an aluminum nitride (AlN) sintered body, and an electronic component 23 such as a semiconductor element, a resistor, or a capacitor is placed on the upper main surface. A mounting portion 22b is formed, and a wiring conductor 22a for inputting / outputting an electric signal to / from the electronic component 23 is formed around the mounting portion 22b.
[0005]
The wiring conductor 22a and the mounting portion 22b are made of a metallized layer formed by firing a conductive paste such as W or Mo, and a metal coating made of a Ni layer having a thickness of 0.5 to 9 μm or an Au layer having a thickness of 0.5 to 5 μm. It is formed by depositing the layer by plating or the like.
[0006]
Further, a thickness of 0.5 to 9 μm is formed on the metallized layer formed by firing a conductive paste such as W or Mo similar to the wiring conductor 22a and the mounting portion 22b over almost the entire lower main surface of the insulating substrate 22. A lower metal layer formed by depositing a metal coating layer made of a Ni layer or an Au layer having a thickness of 0.5 to 5 μm by a plating method or the like is provided. Then, the lower metal layer is brazed to the base 21 via a brazing material such as silver (Ag) brazing (see, for example, Patent Document 1 below).
[0007]
Such a circuit board, after mounting and fixing the electronic component 23 on the mounting portion 22b, electrically connecting the wiring conductor 22a and the electrode of the electronic component 23 via an electrical connection means such as a bonding wire, The overhanging portion 21a of the base body 21 is incorporated into various apparatuses by being fixed to an external electric circuit board or the like by means such as screwing.
[0008]
[Patent Document 1]
Japanese Patent Laid-Open No. 2000-124559
[Problems to be solved by the invention]
However, when the above-mentioned conventional circuit board is fixed to an external electric circuit board or the like by means such as screwing, a bending stress is generated in the overhanging portion 21a, and this bending stress is caused by the root of the overhanging portion 21a. It was easy to join the brazing portion with the insulating substrate 22. When bending stress is applied to the brazing portion, the metal base 21 can plastically deform and absorb the stress, but the ceramic insulating substrate 22 does not plastically deform and becomes a large stress. There was a problem that breakage such as cracks occurred in the insulating substrate 22 near the base of 21a.
[0010]
When the insulation substrate 22 is broken, such as a crack, the wiring conductor 22a is disconnected, and an electric signal cannot be input / output to / from the electronic component 23, and the electronic component 23 cannot operate normally.
[0011]
In addition, even if the damage caused to the insulating substrate 22 is small, the base 21 and the insulating substrate 22 repeatedly contract due to heat generated from the electronic component 23 or an external temperature change, and the damage increases as time passes. And spread to the mounting portion 22b, the electronic component 23 can not be firmly fixed to the insulating substrate 22, or a part of the insulating substrate 22 is dropped and damages the external electric circuit board, etc. There is a problem that the operability of the electronic component 23 is further deteriorated.
[0012]
The present invention has been completed in view of the above problems, and an object of the present invention is to prevent damage to the circuit board and to operate electronic components mounted on the circuit board normally and stably over a long period of time.
[0013]
[Means for Solving the Problems]
The circuit board according to the present invention has a rectangular metal base in which a plurality of projecting portions for external mounting extending outward are formed on the side surfaces, and a plan view shape brazed to the upper surface of the base. An insulating substrate made of ceramics substantially the same as the base, a metal layer formed on a side surface of the insulating substrate located immediately above the overhanging portion, having a width larger than the width of the base of the overhanging portion, and the tensioning And a braze fillet provided from the base of the protruding portion to the metal layer .
[0014]
In the circuit board according to the present invention, the base layer, the insulating substrate, and the insulating substrate are formed by forming a metal layer having a width larger than the width of the base of the overhanging portion at a position located immediately above the overhanging portion of the side surface of the insulating substrate. The braze fillet for brazing can be extended to the metal layer on the side of the insulating substrate, and bent to the overhang when the overhang is fixed to the external electric circuit board by means such as screws. Even if stress occurs, bending stress is effectively absorbed and dispersed by the braze fillet spread on the metal layer, and large stress is locally applied to the brazed part with the base of the overhanging part of the insulating substrate. Can be effectively suppressed. Therefore, even if the protruding portion of the base is fixed to an external electric circuit board or the like by means such as screwing, it is possible to effectively suppress the occurrence of breakage such as a crack in the insulating board.
[0015]
In addition, since the width of the metal layer is larger than the width of the overhanging portion, the area of the joint portion made of the brazing material can be increased, and the stress applied to the brazing portion with the base of the overhanging portion of the insulating substrate is dispersed. The effect to do can be improved more. As a result, the electronic component placed on the circuit board can be operated normally and stably over a long period of time.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
The circuit board of the present invention will be described in detail below. FIG. 1 is a plan view showing an example of an embodiment of a circuit board according to the present invention. In the figure, reference numeral 1 denotes a metal substrate, and 2 denotes a ceramic insulating substrate.
[0017]
In the circuit board of the present invention, a mounting portion 2b and a wiring conductor 2a for mounting electronic components are formed on the upper main surface of an insulating substrate 2 made of ceramics such as an Al ₂ O ₃ sintered body, The lower main surface is brazed with a base body 1 having a protruding portion 1a that extends outward on the side surface and is attached to an external electric circuit board or the like. In addition, a metal layer 2c having a width larger than the width of the base of the overhanging portion 1a is formed in a portion located on the side surface of the insulating substrate 2 immediately above the overhanging portion 1a.
[0018]
The base body 1 is a rectangular flat plate made of a metal such as an Fe—Ni—Co alloy or Cu—W alloy, and is attached to an external electric circuit board or the like that extends outward on the side surface of the base body 1. An overhang portion 1a is provided. The metal base 1 is manufactured in a predetermined shape by subjecting a metal ingot to a conventionally known metal processing method such as rolling or stamping. For example, the base body 1 can be screwed and fixed to the external electric circuit board by providing a through hole for inserting a screw into the overhanging portion 1a.
[0019]
The insulating substrate 2 is made of ceramics such as an Al ₂ O ₃ sintered body, an aluminum nitride (AlN) sintered body, a mullite (3Al ₂ O ₃ · 2SiO ₂ ) sintered body, and the shape in plan view is the base body 1. Is almost the same.
[0020]
Here, “substantially the same” means that the outer periphery of the insulating substrate 2 and the outer periphery of the base body 1 substantially coincide. Therefore, the outer periphery of the insulating substrate 2 may be the same as the outer periphery of the base body 1, and varies depending on the thickness and material of the base body 1, the width of the overhang portion 1 a, etc. It may be. Preferably, the outer periphery of the insulating substrate 2 is outside the outer periphery of the base body 1. As a result, a good braze fillet can be formed over the entire circumference between the lower metal layer formed on the lower surface of the insulating substrate 2 and the side surface of the substrate 1, and the bonding strength between the insulating substrate 2 and the substrate 1 can be increased. It can be improved.
[0021]
Such an insulating substrate 2 is manufactured as follows. For example, in the case of an Al ₂ O ₃ sintered body, first, an organic binder and plasticizer suitable for raw material powders such as Al ₂ O ₃ , silicon oxide (SiO ₂ ), magnesium oxide (MgO), and calcium oxide (CaO). Add a solvent and mix to form a slurry. A plurality of ceramic green sheets are obtained from this by a tape forming technique such as a doctor blade method or a calender roll method.
[0022]
Next, a metal paste obtained by adding and mixing an appropriate organic binder, plasticizer, solvent, etc. to a high melting point metal powder such as W, Mo, etc. is mixed with this ceramic green sheet by a thick film forming technique such as a screen printing method. The wiring conductor 2a, the mounting portion 2b, and the metal layer 2c are formed in a predetermined pattern by printing and coating. Further, a lower metal layer is formed on almost the entire lower surface of the insulating substrate 2. Thereafter, a plurality of ceramic green sheets are laminated and fired at a temperature of about 1600 ° C. in a reducing atmosphere.
[0023]
The wiring conductor 2a and the mounting portion 2b are formed of a metallized layer formed by firing a conductive paste such as W or Mo applied to the upper main surface of the insulating substrate 2, and the surface thereof is prevented from oxidative corrosion. In order to improve the bonding strength with the brazing material, a metal coating layer made of a Ni layer having a thickness of 0.5 to 9 μm or an Au layer having a thickness of 0.5 to 5 μm is preferably applied by a plating method or the like.
[0024]
A lower metal layer for bonding to the base body 1 is formed on the lower main surface of the insulating substrate 2 over the entire surface. This lower metal layer is made of a metallized layer formed by firing a conductive paste such as W or Mo similar to the wiring conductor 2a and mounting portion 2b, and its surface improves the bonding strength with the brazing material. For this purpose, a metal coating layer made of a Ni layer having a thickness of 0.5 to 9 μm or an Au layer having a thickness of 0.5 to 5 μm is preferably deposited by a plating method or the like. Then, this lower metal layer is brazed to the base 1 via a brazing material such as Ag brazing.
[0025]
A metal layer 2c having a width larger than the width of the base of the overhanging portion 1a is formed at a portion located on the side surface of the insulating substrate 2 immediately above the overhanging portion 1a. The metal layer 2c is formed of a metallized layer formed by firing a conductive paste such as W or Mo similar to the wiring conductor 2a and the mounting portion 2b. In order to improve the bonding strength, a metal coating layer made of a Ni layer having a thickness of 0.5 to 9 μm or an Au layer having a thickness of 0.5 to 5 μm is preferably deposited by a plating method or the like.
[0026]
The metal layer 2c is formed in a portion located immediately above the overhanging portion 1a on the side surface of the insulating substrate 2 as shown in a side view in FIG. 2, and at the root of the overhanging portion 1a as shown in FIG. The width W2 is larger than the width W1.
[0027]
Thereby, the fillet of the brazing material for brazing the base body 1 and the insulating substrate 2 can be spread to the metal layer 2c on the side surface of the insulating substrate 2, and the overhanging portion 1a is screwed to the external electric circuit substrate or the like. Even if bending stress is generated in the overhanging portion 1a when fixed by means such as the above, the bending stress is effectively absorbed and dispersed by the braze fillet spreading on the metal layer 2c, and the overhanging portion of the insulating substrate 2 is dispersed. It is possible to effectively prevent a large stress from being locally applied to the brazed portion with the root of 1a. Therefore, even if the protruding portion 1a of the base 1 is fixed to the external electric circuit board or the like by means such as screwing, it is possible to effectively suppress the occurrence of breakage such as cracks in the insulating substrate 2.
[0028]
Further, the width W2 of the metal layer 2c is larger than the width W1 of the overhanging portion 1a, so that the area where the brazing material spreads out can be increased, and the brazing portion with the root of the overhanging portion 1a of the insulating substrate 2 can be increased. The effect of dispersing applied stress can be further improved. As a result, the electronic component 3 placed on the circuit board can be operated normally and stably over a long period of time.
[0029]
Preferably, the width W2 of the metal layer 2c is W1 + 0.1 mm ≦ W2 ≦ 1.5 × W1 with respect to the width W1 of the overhanging portion 1a. When W2 <W1 + 0.1 mm, the area where the brazing material spreads out becomes small, and the effect of relaxing the bending stress applied to the metal layer 2c immediately above the overhanging portion 1a tends to be small. Further, if W2> 1.5 × W1, the width of the metal layer 2c is too large compared to the width of the overhanging portion 1a, and the metal layer 2c is too wet to form a large braze fillet on the metal layer 2c. The effect of absorbing bending stress with the braze fillet tends to be small.
[0030]
As shown in the side view of FIG. 2, the metal layer 2c may be formed between the upper and lower main surfaces of the insulating substrate 2 at a position located immediately above the protruding portion 1a on the side surface of the insulating substrate 2. The side surface of the insulating substrate 2 may be formed only on the lower side of the side surface of the insulating substrate 2 as shown in the side view of FIG. h is preferably h ≧ 0.2 mm. With this configuration, a good braze fillet can be formed on the metal layer 2c, and the bending stress applied to the overhanging portion 1a of the substrate 1 can be dispersed throughout the braze fillet. When h <0.2 mm, the height of the metal layer 2c is too small, the fillet of the brazing material is likely to be small, and the effect of dispersing the bending stress applied to the overhanging portion 1a of the base body 1 is likely to be small.
[0031]
Further, when the metal layer 2 c is positioned at the four corners of the base 1, the metal layer 2 c may be formed from immediately above the protruding portion 1 a on the side surface of the insulating substrate 2 to the adjacent side surface. As a result, a braze fillet is formed so as to cover the corners of the insulating substrate 2 having a low strength. Therefore, it is effective to effectively disperse the stress applied to the corners of the base 1 and to cause cracks in the corners. Can be suppressed.
[0032]
Moreover, as shown in a plan view in FIG. 4, a notch 2d formed in the insulating substrate 2 may be formed along the root of the overhang 1a, and a metal layer 2c may be formed on the inner surface thereof. With this configuration, the surface area of the metal layer 2c can be increased to increase the area where the brazing material spreads, and the brazing material can be stored inside the notch 2d to increase the volume of the brazing filler fillet. Thus, the stress applied to the brazed portion with the base of the overhanging portion 1a of the insulating substrate 2 can be effectively dispersed by the filler fillet. Further, the base 1 positioned between the notch 2d and the overhang 1a can also absorb the bending stress applied to the overhang 1a of the base 1, and the stress relaxation effect is further improved.
[0033]
Such a notch 2d is produced as follows. First, when the insulating substrate 2 is manufactured, a through hole to be a notch 2d is provided in a ceramic green sheet to be the insulating substrate 2, and then the opening of the through hole is covered with a conductive paste. And by attracting | sucking from the back surface of a ceramic green sheet, the conductor paste which covered the opening of the through-hole is made to adhere to an inner surface of a through-hole, and this is baked. Thereafter, the ceramic green sheet is cut so as to divide the through hole, whereby the notched portion 2d having the metal layer 2c on the inner surface can be formed. By forming the metal layer 2c by such a method, workability can be greatly improved as compared with the case where the metal layer 2c is formed directly on the inner surface of the notch 2d by screen printing or brush painting. it can.
[0034]
In this case, the depth d of the notch 2d is preferably 0.1 mm ≦ d ≦ 3 mm. As a result, the bending stress applied to the overhanging portion 1a of the base body 1 is effectively dispersed by the filler fillet of the brazing material, and the bending applied to the overhanging portion 1a of the base body 1 in the base body 1 located below the notch portion 2d. The stress can be absorbed sufficiently. When d <0.1 mm, it is difficult to increase the area of the metal layer 2c, and it becomes difficult to effectively disperse the bending stress applied to the overhanging portion 1a of the base body 1 with the fillet of the brazing material, In the base body 1 below the notch 2d, it may be difficult to sufficiently absorb the bending stress applied to the protruding portion 1a of the base body 1. If d> 3 mm, the insulating substrate 2 must be greatly cut away, and the base body 1 is likely to be deformed and the arrangement of the wiring conductors 2a is likely to be greatly restricted.
[0035]
Such a circuit board, after mounting and fixing the electronic component 3 on the mounting portion 2b, electrically connecting the wiring conductor 2a and the electrode of the electronic component 3 through an electrical connection means such as a bonding wire, The overhanging portion 1a of the base body 1 is incorporated into various apparatuses by being fixed to an external electric circuit board or the like by means such as screwing.
[0036]
According to such a circuit board of the present invention, the metal layer 2c is formed at a position located immediately above the overhanging portion 1a on the side surface of the insulating substrate 2, whereby the base of the overhanging portion 1a of the insulating substrate 2 is formed. A large braze fillet can be formed on the brazing portion of the base plate 1. Therefore, even if the overhanging portion 1a of the base 1 is fixed to the external electric circuit board or the like by means such as screwing, a crack or the like is formed on the insulating substrate 2. Can be effectively prevented from occurring. As a result, the electronic component 3 placed on the circuit board can be operated normally and stably over a long period of time.
[0037]
In addition, this invention is not limited to the example of the above embodiment, A various change is possible if it is in the range which does not deviate from the summary of this invention.
[0038]
【The invention's effect】
The circuit board of the present invention has a quadrangular metal base having a plurality of externally attached overhangs formed on the side surface, and a plan view shape brazed to the upper surface of the base. In the circuit board having a ceramic insulating substrate substantially the same as the insulating substrate, a metal layer having a width larger than the width of the base of the overhanging portion is formed on the insulating substrate at a position directly above the overhanging portion of the side surface. Therefore, the filler fillet for brazing the base body and the insulating substrate can be spread to the metal layer on the side surface of the insulating substrate, and the projecting portion is screwed to the external electric circuit substrate or the like. Even if bending stress is generated at the overhanging part when it is fixed by, the brazing fillet spread over the metal layer effectively absorbs and disperses the bending stress and brazes the base of the overhanging part of the insulating substrate. Effective to apply large stress locally It can be suppressed. Therefore, even if the protruding portion of the base is fixed to the external electric circuit board or the like by means such as screwing, it is possible to effectively suppress the occurrence of breakage such as cracks in the insulating board.
[0039]
In addition, since the width of the metal layer is larger than the width of the overhanging portion, the area of the joint portion made of the brazing material can be increased, and the stress applied to the brazing portion with the base of the overhanging portion of the insulating substrate is dispersed. The effect to do can be improved more. As a result, the electronic component placed on the circuit board can be operated normally and stably over a long period of time.
[Brief description of the drawings]
FIG. 1 is a plan view showing an example of an embodiment of a circuit board according to the present invention.
2 is a side view of the circuit board of FIG. 1. FIG.
FIG. 3 is an enlarged side view of an essential part showing another example of the embodiment of the circuit board of the present invention.
FIG. 4 is a main part enlarged plan view showing another example of the embodiment of the circuit board of the present invention.
FIG. 5 is a plan view of a conventional circuit board.
[Explanation of symbols]
1: Base 1a: Overhanging portion 2: Insulating substrate 2a: Wiring conductor 2b: Placement portion 2c: Metal layer 3: Electronic component

Claims (3)

A quadrangular metal base formed with a plurality of protruding portions for external mounting extending outward on the side surface;
An insulating substrate made of ceramics, which is brazed to the upper surface of the substrate, and whose shape in plan view is substantially the same as that of the substrate;
A metal layer formed on a side surface of the insulating substrate located immediately above the overhang, and having a width larger than the width of the base of the overhang;
A fillet of brazing material provided from the base of the overhang to the metal layer;
A circuit board comprising:   2. The circuit board according to claim 1, wherein the metal layer is formed from immediately above the protruding portion on a side surface of the insulating substrate to a side surface of the adjacent insulating substrate.   The circuit board according to claim 1, wherein the metal layer is formed by depositing a metal coating layer on a surface of a metallized layer.

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